Many systems for producing ceramic powders have been investigated, for example the sol-gel process, plasma processing and other thermal and chemical routes. The sol-gel process is considered to be an expensive process, and some of the other processes have not been successful at producing powders of the required small size or purity.
Numerous attempts at plasma synthesis of materials, such as silicon carbide powder using both an induction plasma and a DC-arc plasma systems have been made. Sub-micron particles of ultra-pure silicon carbide were synthesized at Los Alamos Laboratory (U.S.A.) (see "RF Plasma System for the Production of Ultra-Fine, Ultra-Pure Silicon Carbide" by C. M. Hallbough, Journal of Material Science, Volume 18, 1983, 3190-94), using an RF plasma for reacting silane with methane. O. de Pours, Battell Geneva Research Centre in Ceramic Informazione Volume 13, No. 143, 1978, 283-92 describes production, from the same reactants, of a silicon carbide powder of a particle size of about 0.5 micron was produced using a commercial dc plasma torch. The product was contaminated by copper and tungsten from the torch anode and cathode respectively.
Ultra fine silicon carbide has also been made by a laser driven reaction of silane and methane (see Y. Suyama and R. M. Hara "Synthesis of Ultra-Fine SiC Powder by Laser Driven Gas Phase Reactions", American Ceramics Society Bulletin, V64, No. 10, 1985, 1356-59).
U.S. Pat. No. 4,533,382 issued Aug. 6, 1985 to Miura et al discloses a system for making a fine metal powder using a heated vaporization chamber and cooling the vapour in an adiabatic expansion nozzle to form the powder which is collected in an oil bath. U.S. Pat. No. 4,872,905 produces a metallic or non-metallic powder by a sputtering technique and captures the particles formed in a high molecular weight low vapour pressure oil. The recovered particles have a molecular layer of oil that tends to prevent agglomeration.
Sub-micron size SiC powders are not widely available commercially and those that are have a wide particle size distribution, e.g. ranging between 4 and 0.2 microns.